1. Field of the Invention
The present invention relates to a rubber specimen-stretching jig, an apparatus for analyzing the molecular structure and molecular motion of a stretched rubber specimen, and a method for analyzing the molecular structure and molecular motion of the stretched rubber specimen. More particularly, the present invention is intended to detect a solid high-resolution NMR spectrum of the stretched rubber specimen by rotating it at a magic angle (MAS) so that the molecular structure and molecular motion of the stretched rubber specimen are analyzed.
2. Description of the Related Art
In the development of a rubber product, it is very important to select a rubber material having properties suitable for the rubber product by beforehand analyzing the properties of rubber generated, when the component of the rubber material of the rubber product and the mixing amount of the rubber material are changed. For example, a tire made of the rubber material is demanded to have a contradictory performance that both a rolling resistance and gripping performance thereof are compatible with each other. From the standpoint of satisfying this demand to some extent, it is necessary to analyze properties generated when the rubber material is rotated at a high speed, with the rubber material being stretched.
It is indispensable to know the relationship between the elasticity of rubber and the molecular structure thereof in improving and developing the rubber material. In recent years, the development of the rubber material aimed at revealing novel properties and functions thereof based on a nano-level structure is energetically made.
As explanation of the molecular structure of the revelation of the rubber elasticity, the theory that “The rubber deforms affinely”, namely, the theory that “A deformation of a polymer chain and a macroscopic stretching thereof are proportional to each other” has been widely accepted. But in recent years, reported are many phenomena which cannot be explained by the affine deformation that “The degree of strain of a rubber matrix induced when a rubber material is stretched is not uniform, and when a considerably large load is applied thereto in one direction, 75% of a polymer chain does not orient”. Thus it is now necessary to re-examine the relationship between the rubber elasticity and the molecular structure. To this end, it is necessary to directly observe the molecular structure and molecular motion of the stretched rubber material.
Such being the case, the following apparatus 6 (non-patent document 1) shown in FIG. 8 is proposed. The apparatus is developed to measure a solid 13CNMR of natural rubber when it is tensioned to thereby analyze the molecular structure and molecular motion of the natural rubber when it is tensioned. In the apparatus 6, with both ends of the natural rubber specimen 1 fixed with the wire 2 having a high strength and magnetism. With the specimen 1 being stretched in parallel with the external magnetic field BO by the stretching device 3 fixed to one end of the wire 2, the NMR signal is detected by the saddle-type coil 5, surrounding the specimen 1, which is disposed inside the probe 4 to thereby obtain the solid 13CNMR spectrum.
Because the NMR spectrum of the solid specimen has a very large line width owing to a chemical shift anisotropy of the specimen and an interaction of dipoles, it is impossible to separate signal peaks at respective portions of molecules to be measured. Therefore it is difficult to analyze the structure of the molecules. In relation to this problem, it is known that an anisotropic interaction is removed owing to a magic-angle rotation (MAS) accomplished by a rotation of a specimen tube at a high speed not less than several kHz, with the specimen tube inclined at a certain angle (54.7°) to the static magnetic field BO. Thereby a high-resolution NMR spectrum having a sharp peak is obtained.
In a conventional art shown in FIG. 9, a solid specimen is charged into a cylindrical rotor 7 open at its upper portion. A cap 8 having a blade portion formed thereon is inserted into the rotor 7 by press fit. The cap-mounted rotor 7 is disposed inside a probe (not shown) for rotating the specimen at the magic angle. A gas jetted from a nozzle of a stator (not shown) surrounding the rotor 7 is exerted on the blade portion of the cap 8 to allow the magic rotation (MAS) to be accomplished by rotating the rotor 7 at a high speed.
In the measurement of the solid 13CNMR by using the apparatus disclosed in the non-patent document 1, because the rubber specimen 1 is fixed in a vertically stretched state, it is impossible to measure the solid 13CNMR of the rubber specimen 1 while the rubber specimen 1 is rotating at a high speed. Thus it is difficult to obtain the high-resolution NMR spectrum having a sharp peak. Further because the rubber specimen 1 is fixed in the air, it is impossible to achieve a correct temperature-variable measurement.
In the measurement of the solid 13CNMR to be made by rotating the specimen at the magic angle (MAS), when the specimen is charged nonuniformly inside the rotor 7, the specimen has an unfavorable balance and cannot be rotated at a high speed. Thus it is necessary to uniformly charge the specimen inside the rotor 7. But it is very difficult to uniformly charge the rubber specimen inside the rotor 7 with the rubber specimen stretched.
Non-patent document 1: “Processing of polymer”, third issue of 53 volume (2004) at pages 102 through 107